The present invention relates to an improvement of a power transmission shaft and a propeller shaft that transmit power from a transmission to a driving wheel of a vehicle.
In recent years, there have been proposed and developed various power transmission shafts (propeller shafts). For example, Japanese Patent Application Publication No. 09-123774 (hereinafter is referred to as “JPH09-123774”) discloses in (FIG. 3) a power transmission shaft (a propeller shaft) mounted on a vehicle. The power transmission shaft (the propeller shaft) disclosed in JPH09-123774 has a cylindrical member whose axial direction front end portion is connected to a transmission side of the vehicle and a shaft member whose axial direction rear end portion is connected to a differential carrier side and which is connected to the cylindrical member from an axial direction.
The cylindrical member is provided, on an inner peripheral surface of a rear end portion thereof, with a female spline. The shaft member is provided, on an outer peripheral surface of a front end portion thereof, with a male spline that is inserted into and engaged with the female spline from the axial direction. By the fact that the both splines are engaged from the axial direction, when an excessive input-load is exerted on the cylindrical member from the transmission, for example, upon a collision of the vehicle, the cylindrical member relatively moves toward a direction of the shaft member through the both splines, then shock or impact is lessened.
Further, an inner peripheral seal surface is formed on the inner peripheral surface of the cylindrical member at a tip end side with respect to the female spline of the rear end portion of the cylindrical member. On the other hand, an annular seal groove is formed on the outer peripheral surface of the shaft member at the rear end portion side of the male spline located at the front end portion of the shaft member. Then, a ring-shaped seal ring (a ring-shaped seal member) is provided and an inner peripheral portion of the seal ring is fitted and fixed in the annular seal groove. This ring-shaped seal member is formed as a single-piece ring, and is made of material such as synthetic rubber. An outer peripheral portion of the ring-shaped seal member contacts the inner peripheral seal surface of the cylindrical member by a predetermined elastic force, thereby sealing a contact portion between the shaft member and the cylindrical member.